Coupling device using buried capacitors in multilayered substrate

Abstract

The present invention proposes a coupling device, comprising a substrate ( 1 ), a conductive layer ( 2 ) covering a first surface of said substrate ( 1 ), at least two electromagnetically coupled lines ( 3 a, 3 b ) being provided opposite to said first surface and at least one thereof being covered by at least one cover layer ( 4, 5 ) wherein at least one capacitor (C 1, C 2, C 3, C 4 ) is connected between a first end of at least one of said at least two lines ( 3 a, 3 b ) and said conductive layer ( 2 ). The at least one capacitor is a buried capacitor grounded in order to equalize unequal phase velocities otherwise degrading the performance of e.g. broadside coupled structures in an inhomogeneous substrate structure such as for example microstrips in a multilayer LTCC. Therefore the present invention enables coupling devices having a high performance and offering in that way the best of all possible design scenarios in terms of wideband performance, size and cost.

1. A coupling device, comprising:
 a substrate, 
 a conductive layer covering a first surface of said substrate, 
 at least two electromagnetically coupled lines being provided opposite to said first surface and at least one thereof being covered by at least one cover layer, characterized in that 
 at least one capacitor is connected between a first end of at least one of said at least two lines and said conductive layer, wherein said capacitor is constituted by 
 a conductive member embedded in said substrate and facing said conductive layer covering said first surface of said substrate, and 
 an electrical connection from said first end of said at least one of said at least two lines to said conductive member. 
 
   
   
     2. A coupling device according to  claim 1 , wherein said at least two lines are arranged at different distances from said first surface of said substrate. 
   
   
     3. A coupling device according to  claim 2 , wherein
 a difference between the distances in which said at least two lines are arranged from said first surface of said substrate is determined by a thickness of a first cover layer covering a first line of said at least two lines. 
 
   
   
     4. A coupling device according to  claim 2 , wherein
 a first line and a second line of said at least two lines are arranged such that they at least partly overlap each other. 
 
   
   
     5. A coupling device according to  claim 3 , further comprising:
 a second cover layer arranged to cover at least a second line of said at least two lines. 
 
   
   
     6. A coupling device according to  claim 4 , wherein
 the amount of overlap adjusts the degree of electromagnetic coupling between said at least two lines. 
 
   
   
     7. A coupling device according to  claim 1 , wherein said connection is a via connection. 
   
   
     8. A coupling device according to  claim 1 , wherein the capacitance of said capacitor is determined by the area of said conductive member, the distance between said conductive member and said conductive layer covering said first surface of said substrate, and the dielectric constant of said substrate. 
   
   
     9. A coupling device according to  claim 1 , wherein said at least one cover layer is of the same material as said substrate. 
   
   
     10. A coupling device according to  claim 1 , wherein said substrate is made of a dielectric material. 
   
   
     11. A coupling device according to  claim 1 , wherein said conductive layer is connectable to ground potential.